Infrasound is sound of low frequency, below that which we can hear. Volcanoes produce a lot of infrasound when they explode. Recently it has become a valuable monitoring technique at various volcanoes around the world. The signal produced is less complex that a seismic signal since it passes though the air which has a far less complex structure than the ground. The data can be used to investigate the source mechanism of explosions, pinpoint its origin within a multiple vent system (like Volcán de Colima), and determine depths.